System and methods for increasing fill-factor on pixelated sensor arrays

ABSTRACT

The present invention relates to a system and methodology that facilitates increasing the fill-factor of digital sensor arrays at a reduced cost. In general, fill-factor relates to the active area of the sensor array with respect to the inactive area or space between pixels on the array. By increasing the fill-factor, the present invention enables transmitting maximum amount of optical information to the array while mitigating information loss between pixels on the array. In one aspect of the present invention, an image detector system is provided. The system includes a pixelated sensor array that is responsive to electromagnetic radiation. A coherent scattering medium diffuses the electromagnetic radiation with respect to the pixelated sensor array in order to increase the fill-factor of the array.

TECHNICAL FIELD

The present invention relates generally to image and optical systems,and more particularly to a system and method to facilitate sensor arrayperformance and design by associating a coherent scattering medium witha pixelated sensor array.

BACKGROUND OF THE INVENTION

One area of concern to sensor array manufacturers is that of ensuringthat the active area of their respective products (the pixel) covers themaximum amount of area such that there are substantially no gaps orminimal gaps between pixels. This amount of coverage is usuallydescribed as a percentage “fill-factor” and is computed as follows:fill-factor %=(pixel-pixel area)/(pixel active area)*100. In general, itis very difficult to achieve 100% fill-factor, and in some cases, thearray process generally does not allow a large fill-factor such as isthe case with CMOS sensor technology, for example. There are two primaryreasons for achieving the goal of a high fill-factor which include:

1) To facilitate that a majority of the photons incident on the arrayare captured by the active parts of the array (i.e., increasesensitivity), and,

2) To facilitate that small structures in an image as presented to thearray are not “lost in the spaces between pixels” whereby photonscorrelated with small structures are thus not captured by the activepart of the pixel.

Some manufacturers have attempted to achieve a large effectivefill-factor by the application of arrays of lenslets to the surface ofthe sensor array. This approach has the advantage of increasing theeffective fill-factor and the sensitivity of the array, but suffers fromchromatic effects. Also, lenslet processes by nature pose numerousdifficulties in precise manufacture of micron-sized lenslets, and theassociated problems in precise positioning. Therefore, lenslet stylesolutions add significant cost to the overall production of sensorarrays.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an extensive overview of the invention. It is intended toneither identify key or critical elements of the invention nor delineatethe scope of the invention. Its sole purpose is to present some conceptsof the invention in a simplified form as a prelude to the more detaileddescription that is presented later.

The present invention relates to a system and methodology thatfacilitates imaging performance of digital sensor arrays by associatinga coherent scattering medium or component with a sensor array to achievean optimized fill-factor for the array (e.g., effective 100%fill-factor). The coherent scattering medium acts to diffuse photonsthat may fall in the spaces of the array and thus enable image detailsthat may have been lost by conventional approaches to be detected by thearray. In addition to capturing these details, the present inventionallows for lower cost assembly of sensor arrays by mitigating theaddition of complex components such as lenslets that are also difficultto manufacture and position.

In one aspect of the present invention, a holographic diffuser, forexample, is placed in proximity of a sensor array having a plurality ofpixels (e.g., CMOS array, CCD array, and so forth) such that thediffuser creates a virtual point source with a diffusion angle such thata substantially-sharp point (e.g., infinitely-sharp point) present onthe diffuser is then diffused or spread to cover about one pixel pitchwhich provides coherent spatial coupling between active and inactiveareas of the sensor array. Thus, any information that may have been lostin the spaces between pixels is spread out across inactive or“dead-space” in order to fall on the active portions of the pixels. Inother words, the dead-space has been effectively removed, and the arraycan achieve an “effective 100% fill-factor.” Also, the absoluteresolution of the system can remain unchanged, as a diffused coneemanating from the diffuser can be engineered to generally not covermore than one pixel-pitch and thus preserving resolution.

In a system design example employing the subject diffuser (e.g., camera,copier, fax, microscope, telescope, video), relatively low-cost sensorscan be made to perform (or outperform) very expensive andhigh-fill-factor sensors currently available. Additionally, highlypixelated arrays can be optimized for fill-factor performance byreplacing expensive lenslet arrays with the coherent scattering mediumof the present invention.

The following description and the annexed drawings set forth in detailcertain illustrative aspects of the invention. These aspects areindicative, however, of but a few of the various ways in which theprinciples of the invention may be employed and the present invention isintended to include all such aspects and their equivalents. Otheradvantages and novel features of the invention will become apparent fromthe following detailed description of the invention when considered inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating a coherent couplingsystem and sensor array in accordance with an aspect of the presentinvention.

FIG. 2 illustrates holographic diffuser principles in accordance with anaspect of the present invention.

FIG. 3 illustrates holographic diffuser and sensor design parameters inaccordance with an aspect of the present invention.

FIG. 4 is a flow diagram illustrating a coherent coupling methodology inaccordance with an aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a system and methodology thatfacilitates increasing the fill-factor of digital sensor arrays at areduced cost. In general, fill-factor relates to the active area of thesensor array with respect to the inactive area or space between pixelson the array. By increasing the fill-factor, the present inventionenables transmitting maximum amount of optical information to the activeportions of the array while mitigating information loss between pixelson the array. In one aspect of the present invention, an image detectorsystem is provided. The system includes a pixelated sensor array that isresponsive to electromagnetic radiation such as visible light, forexample. A coherent scattering medium diffuses the electromagneticradiation with respect to the pixelated sensor array in order toincrease the fill-factor of the array.

Systems adapted in accordance with the present invention can includedigital image processing from the respective sensors, if desired, alongwith storage (e.g., local database, image data transmissions to remotecomputers for storage/analysis) and display of the images produced inaccordance with the present invention (e.g., computer display, printer,film, and other output media). Remote signal processing of image datafrom the sensors can be provided, along with communication and displayof the image data via associated data packets that are communicated overa network or other medium, for example.

Referring initially to FIG. 1, a coherent coupling and sensor arraysystem 100 is illustrated in accordance with an aspect of the presentinvention. The system 100 includes a pixelated sensor array 110 (orarray) having one or more receptors such as pixels 114 or discreteenergy detectors operably associated with a coherent scattering medium120. The coherent scattering medium 120 is adapted or configured todisperse or diffuse radiation received from a source 130 (e.g., cameralens) across the pixels 114 on the array 110. As illustrated, energypoints 150 from the source 140 are diffused into e.g., conical patternsat 160. In this manner, by dispersing the energy points 150 at the array110 via the coherent scattering medium 120, the present inventionpromotes an enhanced fill-factor for the array since the energy pointsare captured by the pixels 114 even if the points are not substantiallyaligned with the pixels. Thus, if the coherent scattering medium 120were not present such as in conventional systems, the energy points orspots 150 may fall between the pixels 114 resulting in information beingundetected by the array 110. It is to be appreciated that the coherentscattering medium 120 can produce shapes or patterns such as cones at160 or other shapes that provide coherent spatial coupling betweenactive and inactive areas of the pixelated sensor array 110.

It is noted that the pixelated sensor array 110 can be substantially anysize, shape and/or technology (e.g., digital sensor, analog sensor,Charge Coupled Device (CCD) sensor, CMOS sensor, Charge Injection Device(CID) sensor, an array sensor, a linear scan sensor) including one ormore receptors of various sizes and shapes, the one or more receptorsbeing similarly sized or proportioned on a respective sensor to beresponsive to energy such as light (e.g., visible, non-visible) receivedfrom the source 130. Also, the pixelated sensor array 110 can include anM by N array of pixels associated with the one or more receptors, whereM and N represent integer rows and columns respectively.

As energy is received from the source 130, the array 110 provides anoutput 170 that can be directed to a local or remote storage such as amemory (not shown) and displayed from the memory via a processor andassociated display, for example, without substantially any interveningdigital processing (e.g., straight bit map from sensor memory todisplay), if desired. It is noted that local or remote signal processingof the image data received from the array 110 can also occur. Forexample, the output 170 can be converted to electronic data packets andtransmitted to a remote or local system over a network (wireless orwired) for further analysis and/or display. Similarly, the output 170can be stored in a local computer memory before being transmitted to asubsequent computing system for further analysis and/or display. Imagescan be transferred across the Internet (or other network) such as to acontroller, e-mail address, Ethernet address, or web site, for example.

As will be described in more detail below, the coherent scatteringmedium 120 can be a holographic diffuser in one example that isconfigured to create a diffusion pattern at 160 that is less than aboutthe size of one pixel in the pixelated sensor array 110. It is to beappreciated however, that any coherent scattering medium 120 thatfacilitates coherent coupling of electromagnetic energy within theproximity of the pixelated sensor array 110 is considered to be withinthe scope of the present invention. Also, as can be appreciated, digitaloutput from the array 110 can be employed to perform automated analysisand/or mapped to a display to enable manual inspection of an image.Furthermore, electromagnetic radiation from the source 130 can includesubstantially any type of energy to activate the array 110 such ascoherent light, non-coherent light, visible light and non-visible light(e.g., infrared, ultra violet). In addition, the pixelated sensor array110 and the coherent scattering medium 120 can be associated with aplurality of applications such as a camera, a copier, a fax machine, amicroscope, a telescope, a telephone, handheld device such as a PDA,computer, a watch, and a video application, for example.

Referring now to FIG. 2, holographic diffuser principles are illustratedin accordance with an aspect of the present invention. In a “classical”design approach, such as a digital camera (or other similar instrument),the image is presented to the surface of a sensor array 210 having aplurality of pixels 220 without substantial concern towards correlatingdiffraction-limited spots to the array pixel-pitch, leading to asituation whereby it is possible that the image has spatial structuresthat are smaller than the physical size of the active portions of thepixel. This is illustrated at 230 where light (or energy) from imagingoptics is captured by a sensor pixel and at reference numeral 240 wherelight from the imaging optics is not picked up by the active portions ofthe array 210. In this situation, parts of the image may well beunresolved, not due to diffraction or optical limitations, but due tothe physical dimensions of the array pixels 220.

A holographic diffuser 250 can be positioned near an image plane at 260and prior to a sensor array 270. A diffusion angle for a hologram 280can be computed such that a minimal-sized spot in the image plane (closeto diffraction limited, or at the resolving ability of the lenses) isdiffused to cover about a single pixel interval on the array.Computations for the diffusion angle are described in more detail belowwith respect to FIG. 3. While diffusion may be somewhat achieved with asimple ground glass (or similar) diffuser, the effect will not becomparable, as one of the properties of the holographic diffuser 250 isthat information present at the diffuser surface is equally (orsubstantially equally) distributed over the diffused spot. Thus, forexample, a fine line or other feature that may normally miss the activeportion of a pixel would be diffused such that the information carriedin the line would be available to the active part of the pixel. Apossible side-effect of this may be that sharp images are slightlyblurred, but generally only to the resolution of the array (thepixel-pitch) and thus, substantially no recovered information should belost—on the contrary, extra information should be recovered from the“dead zones” on the array via the holographic diffuser 250. Generally,no intensity should be lost, as the holographic diffuser 250 merelyredistributes photon statistics, and thus, the response of the array 270should not be compromised.

FIG. 3 illustrates holographic diffuser and sensor design parameters inaccordance with an aspect of the present invention. A diffuser 310 canbe selected in accordance with a pixel pitch parameter—(P), illustratedat 320 and a spacing parameter—(S), illustrated at 330. In this case, adiffusion half angle A, can be selected according to the followingequation:Diffusion half angle, A, where Tan(A)=(P/2)/S.

For more precise geometry, one may account for the size of an image spotor point as a parameter (D) or diameter illustrated at 340 along withspacing (S) and pixel pitch (P). In this case, a diffusion half angle A,can be selected according to the following equation:Diffusion half angle, A, where Tan(A)=(P−D)/(2*S).

FIG. 4 illustrates a coherent coupling methodology 400 in accordancewith an aspect of the present invention. While, for purposes ofsimplicity of explanation, the methodology is shown and described as aseries of acts, it is to be understood and appreciated that the presentinvention is not limited by the order of acts, as some acts may, inaccordance with the present invention, occur in different orders and/orconcurrently with other acts from that shown and described herein. Forexample, those skilled in the art will understand and appreciate that amethodology could alternatively be represented as a series ofinterrelated states or events, such as in a state diagram. Moreover, notall illustrated acts may be required to implement a methodology inaccordance with the present invention.

Proceeding to 410, a sensor array is selected. As noted above, this caninclude substantially any type of pixelated sensor array such as a CCDsensor or a CMOS sensor for example. At 420, coherent diffuserparameters are selected. This can include determining pixel pitchdimensions (P), given the sensor characteristics, spacing (S) betweenthe diffuser and the sensor, as well as considerations of spot sizediameters (D), that may be expected at an image plane. From theseparameters, a coherent diffuser such as a holographic diffuser can beselected by determining a diffusion half-angle parameter from theparameters P, S, and/or D. At 430, the coherent diffuser and the sensorare adapted to each other in accordance with the parameters described at420. At 440, the sensor array and associated coherent diffuser areapplied to one or more applications and/or devices. As previously noted,an image can be generated by outputting data from the sensor and storingthe data in memory for direct display to a computer display and/orsubsequent local or remote image processing and/or analysis within thememory.

In accordance with the concepts described above in relation to FIGS.1-4, a plurality of related imaging applications can be enabled andenhanced by the present invention. For example, these applications caninclude but are not limited to imaging, control, inspection, microscopy,telescopes, and/or other analysis such as biomedical analysis (e.g.,cell colony counting, histology, frozen sections, cellular cytology,haematology, pathology, oncology, fluorescence, interference, phase andmany other clinical microscopy applications); particle sizingapplications (e.g., Pharmaceutical manufacturers, paint manufacturers,cosmetics manufacturers, food process engineering, and others); airquality monitoring and airborne particulate measurement (e.g., cleanroom certification, environmental certification, and so forth); opticaldefect analysis, and other requirements for inspection of transmissiveand opaque materials (as in metallurgy, semiconductor inspection andanalysis, machine vision systems and so forth); and imaging technologiessuch as cameras, copiers, fax machines and medical systems, for example.

What has been described above are preferred aspects of the presentinvention. It is, of course, not possible to describe every conceivablecombination of components or methodologies for purposes of describingthe present invention, but one of ordinary skill in the art willrecognize that many further combinations and permutations of the presentinvention are possible. Accordingly, the present invention is intendedto embrace all such alterations, modifications and variations that fallwithin the spirit and scope of the appended claims.

1. An image detector system, comprising: a pixelated sensor arrayresponsive to electromagnetic radiation; and a coherent scatteringmedium to diffuse the electromagnetic radiation with respect to thepixelated sensor array in order to increase the fill-factor of thearray.
 2. The system of claim 1, the coherent scattering medium is aholographic diffuser.
 3. The system of claim 2, the coherent scatteringmedium configured to create a diffusion pattern that is less than aboutthe size of one pixel in the pixelated sensor array.
 4. The system ofclaim 1, the coherent scattering medium is associated with the pixelatedsensor array via the following equation: Tan(A)=(P/2)/S, wherein Arepresents a diffusion half angle, P represents a pixel pitch, and Srepresents a spacing between the coherent scattering medium and thepixelated sensor array.
 5. The system of claim 1, the coherentscattering medium is associated with the pixelated sensor array via thefollowing equation: Tan(A)=(P−D)/(2*S), wherein A represents a diffusionhalf angle, P represents a pixel pitch, S represents a spacing betweenthe coherent scattering medium and the pixelated sensor array, and Drepresents a size of an image spot.
 6. The system of claim 1, thepixelated sensor array being substantially any size and shape, thepixelated sensor array having one or more receptors being substantiallyany size and shape, the one or more receptors being similarly sized andshaped per a given sensor.
 7. The system of claim 6, the pixelatedsensor array further comprising an M by N array of pixels associatedwith the one or more receptors, M and N representing integer rows andcolumns respectively.
 8. The system of claim 1, the pixelated sensorarray further comprising at least one of a digital sensor, an analogsensor, a Charge Coupled Device (CCD) sensor, a CMOS sensor, a ChargeInjection Device (CID) sensor, an array sensor, and a linear scansensor.
 9. The system of claim 1, further comprising a processor and amemory to receive an output from the pixelated sensor array, theprocessor storing the output in the memory.
 10. The system of claim 9,the processor performing automated analysis of the output in the memory.11. The system of claim 9, the processor mapping the memory to a displayto enable manual inspection of an image.
 12. The system of claim 9, theoutput is transmitted across a wireless or wired network to a local or aremote location.
 13. The system of claim 12, the local or remotelocation is associated with an Internet address.
 14. The system of claim1, the electromagnetic radiation includes at least one of coherentlight, non-coherent light, visible light and non-visible light.
 15. Thesystem of claim 14, the non-visible light further comprising at leastone of infrared and ultraviolet wavelengths.
 16. The system of claim 1,the pixelated sensor array and the coherent scattering medium areassociated with at least one of a camera, a copier, a fax machine, amicroscope, a telescope, a telephone, a watch, a handheld device, and avideo application.
 17. A method of producing an image, comprising:determining a pitch size between adjacent pixels on a sensor; andpositioning a coherent diffuser in proximity of the sensor and in viewof the pitch size to facilitate reception of electromagnetic energy bythe pixels.
 18. The method of claim 17, further comprising determining adiameter for an image spot size.
 19. The method of claim 17, furthercomprising employing the sensor and the coherent diffuser with at leastone of a camera, a copier, a fax machine, a microscope, a telescope, ahandheld device, and a video application.
 20. An imaging system,comprising: means for digitally capturing electromagnetic energy; andmeans for dispersing the electromagnetic energy in a coherent manner inorder to mitigate loss of information contained within theelectromagnetic energy.